Re: [Bug] ARM 'perf' regression by commit a43cb95d5

From: Ming Lei
Date: Fri May 17 2013 - 05:27:15 EST

On Fri, May 17, 2013 at 4:55 PM, Will Deacon <will.deacon@xxxxxxx> wrote:
> So it's still the morning and I haven't had my coffee yet, but I'm really
> struggling to see what you're getting at. Why does this have anything to do
> with perf?

I don't know, and I just report it out, :-)

I found the problem days ago, and until yesterday I had one more hours to
git-bisect it, but the result is very frustrated.

>> [1], 'perf top' mistaken output
>> Samples: 17K of event 'cpu-clock', Event count (approx.): 3516532661
>> 97.51% [smsc95xx] [k] 0x013645b8
>> 0.21% [.] strstr
>> 0.14% [.] strchr
>> 0.12% [.] strcmp
> [...]
>> [2], 'perf top' correct output
>> Samples: 46K of event 'cpu-clock', Event count (approx.): 937128704
>> 96.44% [kernel] [k] cpuidle_enter_state
>> 0.19% [.] strstr
>> 0.16% [kernel] [k] kallsyms_expand_symbol.clone.0
>> 0.13% [kernel] [k] _raw_spin_unlock_irq
> [...]
> Are you saying that the profile you're seeing is radically different,
> rather than there being some formatting error that I can't spot? If so, that


> sounds really strange and I can't see how the patch you mention is to
> blame...
> If we want to persue this, I guess other obvious questions are: which kernel
> are you running? Does this affect multiple architectures (your diff only

Either 3.10-rc1 or today's -next tree(3.10.0-rc1-next-20130516).

> changes ARM)? What's the workload which you are profiling?

I only tested it on Pandaboard, and no real workload, so you can see
cpuidle_enter_state is the top frequent symbol.

Or could anyone else try to verify the problem on their own environment?

Ming Lei
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